PREVENTION OF DAMAGE IN WATER HEATING SYSTEMS AND A GUIDELINE FOR WATER TREATMENT INFORMED BY: VDI 2035, PART 2
Closed pipe systems that circulate water will over time be able to experience various problems such as corrosion, growth, precipitation of particles etc.
This can cause two main types of problems. One is weakening and degradation of materials, the other is reduced performance with respect to distribute and transfer heat to or from the circulating liquid.
TWO OF THE MOST CENTRAL ELEMENTS ARE:
- The quality of the circulating water
- The qualities of the materials used
CAUSES OF CORROSION
The most important characteristics of the heating water that determines corrosion are:
1) CONTENT OF DISSOLVED OXYGEN
One. Oxygen (o2) reacts with all metals used in heating systems, and causes oxidization of the metal – also known as corrosion. while air bubbles are visible, it’s not dissolved.
Some oxygen always comes into a system because it will dissolve in the filling water. But if it is able to consistently enter a system in other ways, corrosion damage may be significant.
2) ELECTRICAL CONDUCTIVITY
One. Corrosion is a process that involves a movement of charged particles (metallions and electrones).
Water with high conductivity easiers the corrosion process. demineralized water with low conductivity slows the process. Demineralization of fill water is always recommended.
3) PH
Ph acid (low) ph can attack metals even without the presence of the oxygen. Therefore, an alkaline ph (8.2-10) is recommended. This happens naturally through self-valcalization of metals, so it is normally not necessary to alcalize heat water.
CORROSION PREVENTION
To prevent corrosion damage, the three properties of water quality, sited above, should be checked. The following guidance values should be maintained:
DISSOLVED OXYGEN
<0.1 mg / l (0.1 ppm
ELECTRICAL CONDUCTIVITY <100 /s / cm (tds ~ 67 ppm)
OPERATING PH
8.2-10
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If the system is sealed from oxygen introduction, and keeps a ph in the range of 8.2-10, corrosion should be minimum.
Water treatment with chemicals should be limited to rare cases.
Chemical additives increase conductivity, and when undosage or overdosage it can lead to further corrosion.
In cases of avoidable oxygen introduction, electrocemical treatment is preferred.
If the system is sealed from oxygen introduction, and keeps a ph in the range of 8.2-10, corrosion should be minimum.
Water treatment with chemicals should be limited to rare cases.
Chemical additives increase conductivity, and when undosage or overdosage it can lead to further corrosion.
In cases of avoidable oxygen introduction, electrocemical treatment is preferred.
The magnesium anode is "sacrificed" for the benefit of the rest of the plant.
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